Orthopedic cables are used to strengthen and repair broken bones. The cables are typically formed into a loop, simple or complex, and tightened about the bone structure with a tensioning tool. See for example Songer et al. U.S. Pat. No. 5,116,340.
There remains a need for a cable tensioner which has a narrow, thin design so that it can penetrate into small, deep wounds and incisions for tensioning of cables deeply mounted in the body.
Also, it would be desirable to provide a cable tensioning unit having the flexibility to engage a wide variety of different cable crimps, as well as being usable in other cable tensioning operations. For example, the cable tensioner might press against a bone plate rather than holding a crimp in the cable tensioning process.
By this invention, such a narrow, thin, but versatile cable tensioner is provided which is capable of gripping a wide variety of cable crimps, or merely providing pressure against bone plates or the like as part of the tensioning process.
The cable tensioner apparatus is also capable of providing a specific, predetermined level of tension which may be variable on a moment-to-moment basis as the surgeon may decide. Also, the process of the tensioning is convenient in its operation and quick.
By this invention a cable tensioning device is provided which comprises: a tubular shaft having an outer threaded portion and a handle member surrounding a portion of the shaft. The handle member carries the shaft in a manner permitting a relative rotation which causes the shaft to move longitudinally relative to the handle as the handle rotates. This is preferably accomplished by connecting the tubular shaft and handle member together in screw-threaded relation.
A gripping member is carried on the shaft distal to the handle member for holding a cable crimp, typically by use of a replaceable bit which, in turn, can releasably carry a cable crimp or be otherwise used in a crimping function, for example by pressing against a bone plate to provide purchase for tensioning. The bit is replaceable, typically in a conventional manner of tool bits, so that different bits may be used for receiving different cable crimps or for performing other desired tensioning functions.
A cable lock is positioned on a portion of the tensioning device which is typically proximal to the handle member, and does not rotate with the handle member, to hold the ends of cables extending through the tubular shaft. Any suitable conventional cable lock mechanism may be used.
Accordingly, rotation of the handle member can cause the shaft to move longitudinally without rotation, to lengthen the distance between the cable lock and the bit which is held by the gripping member, to impose a tension on the cable.
Also, a meter, carried by the tensioning device, is provided for measuring the tension, so that the surgeon can apply a specific, quantitative tension as desired to a cable by means of the tensioning device of this invention.
The handle member preferably defines a bore having an internally threaded section of no more than about 180 degrees extent around the bore, and typically less. The tubular shaft extends through the bore and defines external threads that normally engage the internally threaded section. Means, such as a spring-biased push button, are provided for temporarily moving the internally threaded section out of engagement with the external threads, to permit the shaft to freely slide in the bore of the handle member. Thus, when tensioning is desired, the threads may be disengaged and the shaft may be manually extended from the handle member to a position where the tensioning begins. Then, the threads may be reengaged, and the handle rotated to provide a quantitatively determinable tension (through the meter) on the cable as desired. Thus, a substantial saving in time is provided by this means for temporarily moving the internally threaded section out of engagement with the external threads, so that the shaft may be quickly advanced to the position where tensioning of the cable begins.
The meter typically comprises a longitudinally sliding portion of the device, relative to the handle member, typically positioned at the proximal end of the meter. A spring is positioned to resist sliding of this portion toward the gripping member. An indicator or meter is provided of the amount of such sliding as the cable is tensioned, responsive to the degree of deflection of the spring. Because the cable lock is carried on this sliding portion, increased tension of the cable results in more deflection of the spring. The indicator may be an arrow which slides along a scale, indicating the quantitative amount of tension as the spring is depressed by that tension.